1. Field of the Invention
The present invention relates to control methods, control systems and programs, and more particularly to a control method and a control system that control the performance of a predetermined apparatus, and a program that makes a computer that controls the performance of the predetermined apparatus execute a predetermined procedure.
2. Description of the Background Art
Conventionally, in a lithographic process for manufacturing microdevices such as semiconductor devices (integrated circuits), liquid-crystal display devices, imaging devices such as CCD, and thin film magnetic heads, various types of exposure apparatuses to form a circuit pattern on an object to be exposed such as a wafer or a glass plate (hereinafter generally referred to as a ‘wafer’) have been used. In recent years, due to higher integration of semiconductor devices, the increase in size of a wafer and the like, in order to transfer a fine pattern on a wafer with high throughput, sequentially moving type projection exposure apparatuses are mainly used, such as a reduction projection exposure apparatus by a step-and-repeat method (the so-called stepper) or a scanning projection exposure apparatus by a step-and-scan method (the so-called scanning stepper (also called as a ‘scanner’)) that is an improvement of the stepper.
When manufacturing microdevices such as semiconductor devices, it is normal to perform overlay exposure in order to form and overlay multiple layers of different circuit patterns on a wafer. Therefore, as basic capability to mass-produce microdevices of higher integration, a projection exposure apparatus requires not only throughput but also high overlay accuracy (relative position accuracy when forming a pattern on a wafer and further forming another pattern on the wafer in the next process).
In order to constantly maximize the capability, in the projection exposure apparatus, performance control of various types is performed by periodic maintenance and the like. For improving the overlay accuracy, it is necessary to maintain the image-forming performance of a projection optical system in good condition as well as high resolution. The control of the image-forming performance of the projection optical system, as an example, the control of focus has been performed as follows.
a. Measurement of a best focus position of the projection optical system is executed with predetermined frequency, for example, once a day. In the measurement, an aerial image measurement, in which a projected image (an aerial image) of a measurement mark by a projection optical system is measured using an aerial image measurement unit. At least a part of the aerial image measurement unit is arranged on a wafer stage on which a wafer is mounted, and the aerial measurement is repeatedly performed while changing the position of the wafer stage in an optical axis direction of the projection optical system in predetermined pitch, and the best focus position of the projection optical system is measured in a predetermined method based on each aerial image intensity signal that is obtained as a result of the aerial measurement (refer to Kokai (Japanese Unexamined Patent Application Publication) No. 2002-014005).
b. A focus variation amount that is obtained as a result of the above ‘a’ is compared with a permissible value set in advance, and in the case the focus variation amount exceeds the permissible value, the focus variation mount is confirmed by a test exposure. The best focus has been determined by the test exposure as follows.
That is, first, an image of a focus measurement mark is transferred to different positions on the wafer, while changing the position of the wafer stage in the optical axis direction in a predetermined pitch or changing an exposure amount (a dose amount) irradiated onto the wafer by a predetermined amount. Next, the wafer is developed, and a matrix (which is called a focus-exposure amount matrix (FEM)) is formed on the wafer. The matrix has, as an element, an area where transferred images (resist images) of the focus measurement mark at different positions of the wafer stage in the optical axis direction or the transferred images of the focus measurement mark with different dose amounts are formed, and the focus position that corresponds to a row in which a finest pattern is resolved among the rows of the matrix is to be the best focus position (refer to Kokai (Japanese Unexamined Patent Application Publication) No. 09-320945).
c. Then, based on the obtained best focus position, calibration of a focus sensor is executed.
In the method above, when the best focus position is to be controlled with higher accuracy, the permissible value described earlier needs to be smaller. However, when the permissible value becomes smaller, the focus variation amount obtained as the result of ‘a’ exceeds the permissible value and confirmation of the focus variation amount by the test exposure described above (such as exposure, development, and measurement of a resist image) is performed, almost every time.
In the case periodic exposure, development, measurement of a resist image and the like are performed for the check of the best focus position, however, the measurement takes a long period of time, which necessarily leads to the increase in downtime of the apparatus. The control of image-forming performances of the projection optical system besides the best focus position can be performed by combining the aerial image measurement and the test exposure in the same manner as described above.
Further, besides the image-forming performances of the projection optical system, for example, in order to control the position control performance of a stage (including synchronization accuracy of a reticle stage and a wafer stage in the case of the scanner), a check operation of the position control performance by the same test exposure as is described above has been performed periodically (for example, every few days). Therefore, the measurement takes a long period of time, which necessarily leads to the increase in downtime of the apparatus.
Against the background described above, a new system or the like is expected that can control with high accuracy the image-forming performances of projection optical systems, the position control performance of stages and other performances of exposure apparatuses, and also can reduce downtime of the apparatus.